In observation or treatment of a body lumen or the like by use of an endoscope, a guide wire is used for guiding the endoscope or a catheter inserted in the lumen of the endoscope to a predetermined position in the body lumen or the like.
In inserting the guide wire, a movement of the guide wire in the axial direction cannot be sensed if the guide wire is monochromatic; therefore, it is preferable that a marker indicative of position or the like is provided on the surface of the guide wire. In view of this, methods for providing guide wires with various marks have hitherto been proposed.
For example, a method has been known in which a hollow tube formed of polytetrafluoroethylene or the like and having a plurality of colored stripes is adhered to a distal portion of a core member of a guide wire by putting the hollow tube over the distal portion in an enveloping manner through heat shrinkage (see, for example, Patent Document 1).
Since there is a limit to the shrinkage of the hollow tube, however, it is impossible by this method to render the wall portion of the tube sufficiently thin, even by application of heat shrinkage to the tube. Therefore, flexibility of the distal portion of the guide wire is not secured sufficiently, so that the distal portion would be too hard to be inserted into a living body. Besides, in this method, adhesion of the hollow tube onto the core member is performed through the steps of inserting the core member into the hollow tube and, further, heating the hollow tube in this condition. Consequently, the guide wire manufacturing process would be complicated, and the manufacturing cost would be increased.
Besides, in the guide wire described in Patent Document 1, by preparing the hollow tube which has a light color and adhering the hollow tube onto the core member, it is possible to ensure that the marker composed of the hollow tube has an enhanced contrast. However, the guide wire described in Patent Document 1 is poor in flexibility, as above-mentioned.
In view of this problem, in Patent Document 1, not only the configuration in which the marker is composed of the hollow tube as above-mentioned is described, but also a method is mentioned in which a member obtained by applying a coating material to a distal portion of the core member and drying the coating material is made to function as a marker. In this case, it may be possible to secure flexibility of the distal portion of the guide wire as much as possible, but the marker would be discolored into a color difficult to visually confirm (for example, a blackish deep blue). The reason for discoloration into such a color may be as follows.
As the coating material to be applied, there may be contemplated one which contains a low-friction material, a pigment and a binder resin material, and in which, particularly, the binder resin material among these constituent materials is contained in a large amount. In this case, during drying of the coating material, the binder resin material may be discolored, for example, to yellow or liver brown or the like color by the heat for drying. As a result, the marker obtained would have a mixed color of the color of the discolored binder resin material and the color of the pigment, in other words, would appear to have been discolored into a color difficult to visually confirm.
Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei 9-501593